2008 what? They made the 660 and 700 and a few other Grizzly models then. My 660 has a small tab on the back of the seat that you lift then lift the back of the seat and pull toward the rear to get the seat off. I am surprised you are having trouble. Good luck!
Edit: I can't believe it's two of the newer guys with '02 660's to the rescue! Lol!